1. Field of the Invention
The present invention relates to a method of manufacturing an organic electroluminescence (EL) device.
2. Description of the Related Art
A generally known display device (display) having organic EL elements mounted thereon is a device in which pixels each including a single or multiple organic EL elements are arranged in a predetermined pattern. In such case, the organic EL elements included in the pixels are electronic elements which output, for example, any one of red light, green light, and blue light. A display device having organic EL elements mounted thereon obtains a full-color image by driving the organic EL elements for outputting desired colors at desired emission intensities.
By the way, in an organic EL element which is a component of a display device, an organic compound layer included in the element is a thin film layer formed by forming a thin film made of an organic material by vapor deposition or the like. When the organic compound layer which is included in the organic EL element of the display device is formed for each of the elements, a fine patterning technology is necessary. When patterning is carried out in vapor deposition, a fine metal mask corresponding to the fineness of the patterning is necessary. However, when a metal mask is repeatedly used for vapor deposition, a vapor deposited film may adhere to narrow an opening in the mask, or stress may deform the opening in the mask. Therefore, it is necessary to clean the used mask after performing film formation for a fixed number of times, which is a disadvantageous factor from the viewpoint of manufacturing costs. In addition, due to a limitation on the process accuracy of the mask, the pixel size has a limit of about 100 μm, which is disadvantageous to a finer size of a display device. Further, in terms of the substrate size, when a fine metal mask is increased in size, in order to secure the positional accuracy of the opening in the mask, it is necessary to enhance the stiffness of a frame of the mask. However, when the stiffness of the mask is enhanced, the weight of the mask itself is increased accordingly. Therefore, from the viewpoint of both processability and handling, it is difficult to manufacture large display device of the fourth and subsequent generations, and an optimum manufacturing process of a fine organic EL element and a display device having the organic EL element mounted thereon has not taken shape at present.
Under those circumstances, there has been proposed a method of manufacturing a display device including a fine organic EL element without using a metal mask. Methods proposed in Japanese Patent Application Laid-Open No. 2006-164993 and Japanese Patent No. 3839276 are specific examples of such a method. The methods proposed in Japanese Patent Application Laid-Open No. 2006-164993 and Japanese Patent No. 3839276 are methods involving, after repeating three times for the respective colors a step of patterning by photolithography an organic compound layer formed on an entire surface of a substrate to leave the organic compound layer only in a predetermined location, forming a common electrode.
By the way, in the methods (manufacturing methods) proposed in Japanese Patent Application Laid-Open No. 2006-164993 and Japanese Patent No. 3839276, an organic EL layer is patterned by the process including the following steps of:
(a) forming an organic EL layer and a photoresist layer in this order on an entire surface of an emission region on a substrate having a lower electrode formed thereon;
(b) exposing a part of the photoresist layer in accordance with the pattern of the organic EL layer;
(c) removing by developing treatment a part of the photoresist layer which is not exposed; and
(d) removing by etching treatment a part of the organic EL layer provided in a region in which the photoresist layer is removed in the step (c).
According to the process, the photoresist layer provided in patterning is in a state of being selectively provided on the patterned organic EL layer, and thus, the photoresist layer may be easily released. After the photoresist layer is released, an upper electrode (common electrode) is formed.
By the way, when an organic EL device manufactured by the process including the above-mentioned steps (a) to (d) includes multiple kinds of organic EL elements which emit light of different colors, the process including the above-mentioned steps (a) to (d) is repeated for each kind. Then, a region in which no organic EL element is provided, for example, a pixel division layer (bank) provided between elements is subjected to the etching in the above-mentioned step (d) multiple times. Here, the pixel division layer (bank) provided in a region between elements and the like are not protected by the photoresist layer, and are thus subjected to the etching in the above-mentioned step (d). In a display in which organic EL elements of three colors, i.e., RGB, are arranged, when the above-mentioned patterning process (steps (a) to (d)) is carried out three times, members such as the pixel division layer (bank) are subjected to the etching three times at the maximum.
On the other hand, members such as the pixel division layer (bank) provided in a region between elements are usually formed of an insulating resin material such as a polyimide-based resin material or an acrylic-based resin material. The above-mentioned resin material is a hydrocarbon-based material including heteroatoms (such as oxygen atoms or nitrogen atoms) or not including heteroatoms. Therefore, in the etching in the above-mentioned step (d), such members may be etched at an etching rate which is equal to that of the organic EL layer. Then, a part of the members such as the pixel division layer is etched away to form a groove. If such a groove is formed, when the upper electrode (common electrode) to be provided on the entire surface of the emission region is formed after the organic EL layer is formed, a part of the upper electrode may be broken due to a step caused by the groove.
Further, when organic EL elements are arranged in a display device in a high density, it is preferred that wiring for inputting a drive signal to each of the organic EL elements be formed under an insulating layer such as the pixel division layer to electrically connect the wiring to a circuit for driving each of the organic EL elements and the like. In a case where a conductive layer such as an electrode layer or a wiring layer is formed under the insulating layer in this way, when the insulating layer is locally removed to a deep level by etching, the electrode layer or the conductive layer arranged under the insulating layer is exposed. Then, a short circuit may be caused with the upper electrode when the upper electrode is formed.